Acoustic wave device with multi-layer substrate including ceramic

ABSTRACT

An acoustic wave device is disclosed. The acoustic wave device includes a support layer, a ceramic layer positioned over the support layer, a piezoelectric layer positioned over the ceramic layer, and an interdigital transducer electrode positioned over the piezoelectric layer. The support layer has a higher thermal conductivity than the ceramic layer. The ceramic layer can be a polycrystalline spinel layer. The acoustic wave device can be a surface acoustic wave device configured to generate a surface acoustic wave.

CROSS REFERENCE TO PRIORITY APPLICATIONS

This application claims the benefit of priority of U.S. ProvisionalPatent Application No. 62/810,649, filed Feb. 26, 2019 and titled“SURFACE ACOUSTIC WAVE RESONATOR WITH SUBSTRATE INCLUDING SPINEL LAYER,”and U.S. Provisional Patent Application No. 62/810,707, filed Feb. 26,2019 and titled “SURFACE ACOUSTIC WAVE RESONATOR WITH MULTI-LAYERSUBSTRATE INCLUDING SPINEL,” the disclosures of each of which are herebyincorporated by reference in their entireties herein.

BACKGROUND Technical Field

Embodiments of this disclosure relate to acoustic wave devices.

Description of Related Technology

Acoustic wave filters can be implemented in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include acoustic wave filters. An acoustic wave filtercan filter a radio frequency signal. An acoustic wave filter can be aband pass filter. A plurality of acoustic wave filters can be arrangedas a multiplexer. For example, two acoustic wave filters can be arrangedas a duplexer.

An acoustic wave filter can include a plurality of resonators arrangedto filter a radio frequency signal. Example acoustic wave filtersinclude surface acoustic wave (SAW) filters and bulk acoustic wave (BAW)filters. A surface acoustic wave resonator can include an interdigitaltransductor electrode on a piezoelectric substrate. The surface acousticwave resonator can generate a surface acoustic wave on a surface of thepiezoelectric layer on which the interdigital transductor electrode isdisposed.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The innovations described in the claims each have several aspects, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope of the claims, some prominent features ofthis disclosure will now be briefly described.

In one aspect, an acoustic wave device is disclosed. The acoustic wavedevice can include a support substrate, a ceramic layer positioned overthe support substrate, a piezoelectric layer positioned over the ceramiclayer, and an interdigital transducer electrode positioned over thepiezoelectric layer. The support substrate has a higher thermalconductivity than the ceramic layer. The acoustic wave device configuredto generate an acoustic wave.

In an embodiment, the support substrate is a single crystal layer.

In an embodiment, the support substrate includes silicon.

In an embodiment, the acoustic wave has a wavelength of λ, and thepiezoelectric layer has a thickness in a range from 3λ, to 40λ.

In an embodiment, the acoustic wave has a wavelength of λ, and athickness of the piezoelectric layer is at least 5λ.

In an embodiment, the ceramic layer includes polycrystalline spinel.

In an embodiment, a surface of the ceramic layer has a maximum surfaceroughness of 2 nanometers or less.

In an embodiment, the surface of the ceramic layer has a surfaceroughness in a range from 0.1 nanometers to 2 nanometers. The ceramiclayer and the piezoelectric layer can be directly bonded to each otherwithout an intervening layer.

In an embodiment, a surface of the ceramic layer has an average surfaceroughness of 1 nanometers or less.

In an embodiment, the ceramic layer and the support substrate are bondedto each other by way of an adhesive. The adhesive can include at leastone of aluminum, titanium, or a nitride.

In an embodiment, the acoustic wave device further includes atemperature compensation layer over the interdigital transducerelectrode.

In an embodiment, the interdigital transducer electrode includes twolayers. One of the two layers can include aluminum. The other of the twolayers can include molybdenum.

In an embodiment, the piezoelectric layer includes lithium basedpiezoelectric layer.

In an embodiment, the ceramic layer is arranged to scatter backreflections of the acoustic wave.

In an embodiment, the support substrate is thicker than the ceramiclayer.

In an embodiment, a surface acoustic wave filter includes the surfaceacoustic wave resonators that is arranged to filter a radio frequencysignal. A front end module can include the surface acoustic wave filter,other circuitry, and a package that encloses the surface acoustic wavefilter and the other circuitry. The other circuitry can include amulti-throw radio frequency switch. The other circuitry can include apower amplifier. A wireless communication device can include an antennaand the surface acoustic wave filter. The surface acoustic wave filtercan be arranged to filter a radio frequency signal associated with theantenna.

In one aspect, an acoustic wave device is disclosed. The acoustic wavedevice can include a support substrate, a polycrystalline spinel layerpositioned over the support substrate, a piezoelectric layer positionedover the polycrystalline spinel layer, and an interdigital transducerelectrode positioned over the piezoelectric layer. The support substratehas a greater thermal conductivity than the polycrystalline spinellayer. The acoustic wave resonator is configured to generate an acousticwave.

In an embodiment, the acoustic wave device further includes atemperature compensation layer positioned over the interdigitaltransducer electrode. The temperature compensation layer can be asilicon dioxide layer.

In an embodiment, the support substrate is monocrystalline.

In an embodiment, the support substrate includes silicon.

In an embodiment, the support substrate includes sapphire.

In an embodiment, the support substrate is thicker than thepolycrystalline spinel layer.

In an embodiment, a surface of the polycrystalline spinel layer has amaximum roughness of 2 nanometers or less.

In an embodiment, the surface of the polycrystalline spinel layer has asurface roughness in a range from 0.1 nanometers to 2 nanometers. Thepolycrystalline spinel layer and the piezoelectric layer can be bondedto each other without an intervening layer.

In an embodiment, a surface of the support substrate has an averageroughness of 2 nanometers or less. The polycrystalline spinel layer andthe support substrate can be bonded to each other without an interveningadhesive.

In an embodiment, the acoustic wave device further includes an adhesivelayer between the polycrystalline spinel layer and the supportsubstrate. The adhesive layer can include at least one of aluminum,titanium, or a nitride. The adhesive layer can have a greater thermalconductivity than the polycrystalline spinel layer.

In an embodiment, the acoustic wave has a wavelength of λ, and thepiezoelectric layer has a thickness in a range from 3λ, to 40λ

In an embodiment, the surface acoustic wave has a wavelength of λ, and athickness of the piezoelectric layer is at least 5λ.

In an embodiment, the interdigital transducer electrode includes twolayers. One of the two layers can include aluminum. The other of the twolayers can include molybdenum.

In an embodiment, the piezoelectric layer includes lithium niobate.

In an embodiment, a surface acoustic wave filter includes surfaceacoustic wave resonators arranged to filter a radio frequency signal.The surface acoustic wave resonators including the surface acoustic waveresonator. A front end module can include the surface acoustic wavefilter, other circuitry, and a package that encloses the surfaceacoustic wave filter and the other circuitry. The other circuitry cabinclude a multi-throw radio frequency switch. The other circuitry caninclude a power amplifier. A wireless communication device comprising anantenna and the surface acoustic wave filter. The surface acoustic wavefilter can be arranged to filter a radio frequency signal associatedwith the antenna.

In one aspect, a surface acoustic wave filter is disclosed. The surfaceacoustic wave filter can include a surface acoustic wave resonator. Thesurface acoustic wave resonator can include a support substrate, aceramic layer positioned over the support substrate, a piezoelectriclayer positioned over the ceramic layer, and an interdigital transducerelectrode positioned over the piezoelectric layer. the surface acousticwave filter can also include a plurality of other surface acoustic waveresonators. The surface acoustic wave resonator and the plurality ofother surface acoustic wave resonators are together arranged to filter aradio frequency signal.

In an embodiment, the ceramic layer is a polycrystalline spinel layer.

In an embodiment, a front end module includes the surface acoustic wavefilter, other circuitry, and a package that encloses the surfaceacoustic wave filter and the other circuitry. The other circuitry caninclude a multi-throw radio frequency switch. The other circuitryincludes a power amplifier.

In an embodiment, a wireless communication device comprising an antennaand the surface acoustic wave filter. The surface acoustic wave filtercan be arranged to filter a radio frequency signal associated with theantenna.

In one aspect, a method of manufacturing an acoustic wave device isdisclosed. The method can include attaching a support substrate to aceramic layer. The support substrate has a higher thermal conductivitythan the ceramic layer. The method can also include bonding apiezoelectric layer to a surface of the ceramic layer such that thepiezoelectric layer and the support substrate are on opposing sides ofthe ceramic layer. The method can further include forming aninterdigital transducer electrode over the piezoelectric layer. Theacoustic wave device includes the support substrate, the ceramic layer,the piezoelectric layer, and the interdigital transducer electrode.

In an embodiment, the support substrate includes silicon.

In an embodiment, the method further includes smoothing the surface ofthe ceramic layer prior to the bonding. The surface of the ceramic layercan have a maximum surface roughness of 2 nanometers or less after thesmoothing. The surface of the ceramic layer can have an average surfaceroughness of 1 nanometer or less. The smoothing can includechemical-mechanical polishing.

In an embodiment, the method further includes smoothing a surface of thesupport substrate prior to the attaching.

In an embodiment, the method further includes smoothing a second surfaceof the ceramic layer prior to the attaching. The second surface of theceramic layer is opposite to the surface of the ceramic layer.

In an embodiment, the attaching includes applying an adhesive betweenthe support substrate and the ceramic layer.

In an embodiment, the attaching the support substrate to the ceramiclayer includes direct bonding.

In an embodiment, the bonding the piezoelectric layer and the ceramiclayer includes direct bonding.

In an embodiment, the acoustic wave device is a surface acoustic waveresonator of a surface acoustic wave filter.

In one aspect, a method of manufacturing an acoustic wave device isdisclosed. The method can include attaching a support substrate to apolycrystalline spinel layer. The support substrate has a higher thermalconductivity than the polycrystalline spinel layer. The method can alsoinclude bonding a piezoelectric layer to a surface of thepolycrystalline spinel layer such that the piezoelectric layer and thesupport substrate are on opposing sides of the polycrystalline spinellayer. The method can further include forming an interdigital transducerelectrode over the piezoelectric layer.

In an embodiment, the method further includes smoothing the surface ofthe polycrystalline spinel layer prior to the bonding. The surface ofthe polycrystalline spinel can have a surface roughness in a range from0.1 to 2 nanometers after the smoothing. The surface of thepolycrystalline layer can have an average surface roughness of 1nanometer or less. The surface of the polycrystalline layer can have asurface roughness in a range from 0.1 nanometers to 2 nanometers. Thesmoothing can include chemical-mechanical polishing.

In an embodiment, the method further includes smoothing a surface of thesupport substrate prior to the attaching.

In an embodiment, the method further includes smoothing a second surfacethe polycrystalline spinel layer prior to the attaching. The secondsurface of the polycrystalline spinel layer is opposite to the surfaceof the polycrystalline spinel layer.

In an embodiment, the attaching includes applying an adhesive betweenthe support substrate and the polycrystalline spinel layer.

In an embodiment, the attaching the support substrate to thepolycrystalline spinel layer includes direct bonding.

In an embodiment, the bonding the piezoelectric layer and thepolycrystalline spinel layer includes direct bonding.

In an embodiment, the method further includes forming a temperaturecompensation layer over the interdigital transducer electrode.

In one aspect, a method of manufacturing a surface acoustic wave filterfor filtering a radio frequency signal is disclosed. The method caninclude attaching a support substrate to a ceramic layer. The supportlayer has a higher thermal conductivity than the ceramic layer. Themethod can also include bonding a piezoelectric layer to a surface ofthe ceramic layer. The method can also include forming an interdigitaltransducer electrode over the piezoelectric layer. A surface acousticwave resonator includes the interdigital transducer electrode. Themethod can further include electrically connecting the surface acousticwave resonator to another surface acoustic wave resonator of the surfaceacoustic wave filter.

In an embodiment, the ceramic layer is a polycrystalline spinel layer.

The present disclosure relates to U.S. Patent Application Ser. No.16/800,391, titled “METHOD OF MANUFACTURING ACOUSTIC WAVE DEVICE WITHMULTI-LAYER SUBSTRATE INCLUDING CERAMIC,” filed on even date herewith,the entire disclosure of which is hereby incorporated by referenceherein.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the innovations have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment. Thus, theinnovations may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other advantages as may be taught or suggestedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1 illustrates a cross section of a surface acoustic wave (SAW)resonator that includes a polycrystalline spinel layer according to anembodiment.

FIG. 2A illustrates a cross section of a surface acoustic wave resonatorthat includes a polycrystalline spinel layer according to anotherembodiment.

FIG. 2B is a thermal map of a SAW chip that includes a SAW resonator ofFIG. 2A.

FIG. 3 is a graph of a thermal simulation result of a SAW resonator.

FIG. 4 illustrates a cross section of a surface acoustic wave resonatoraccording to an embodiment.

FIG. 5 illustrates a cross section of a surface acoustic wave resonatoraccording to another embodiment.

FIG. 6A is a flow chart that illustrates a manufacturing process offorming a SAW resonator according to an embodiment.

FIG. 6B is a flow chart that illustrates another manufacturing processof forming a SAW resonator according to an embodiment.

FIG. 7A illustrates a cross section of a SAW resonator at a step in amanufacturing process, according to embodiment.

FIG. 7B illustrates a cross sections of a SAW resonator at another stepin the manufacturing process.

FIG. 7C illustrates a cross sections of a SAW resonator at another stepin the manufacturing process.

FIG. 7D illustrates a cross sections of a SAW resonator at another stepin the manufacturing process.

FIG. 8A is a schematic diagram of a transmit filter that includes asurface acoustic wave resonator according to an embodiment.

FIG. 8B is a schematic diagram of a receive filter that includes asurface acoustic wave resonator according to an embodiment.

FIG. 9 is a schematic diagram of a radio frequency module that includesa surface acoustic wave resonator according to an embodiment.

FIG. 10 is a schematic diagram of a radio frequency module that includesfilters with surface acoustic wave resonators according to anembodiment.

FIG. 11 is a schematic block diagram of a module that includes anantenna switch and duplexers that include a surface acoustic waveresonator according to an embodiment.

FIG. 12A is a schematic block diagram of a module that includes a poweramplifier, a radio frequency switch, and duplexers that include asurface acoustic wave resonator according to an embodiment.

FIG. 12B is a schematic block diagram of a module that includes filters,a radio frequency switch, and a low noise amplifier according to anembodiment.

FIG. 13A is a schematic block diagram of a wireless communication devicethat includes a filter with a surface acoustic wave resonator inaccordance with one or more embodiments.

FIG. 13B is a schematic block diagram of another wireless communicationdevice that includes a filter with a surface acoustic wave resonator inaccordance with one or more embodiments.

FIG. 14 is a schematic diagram of one example of a communicationnetwork.

FIG. 15A is a schematic diagram of one example of a communication linkusing carrier aggregation.

FIG. 15B illustrates various examples of uplink carrier aggregation forthe communication link of FIG. 2A.

FIG. 15C illustrates various examples of downlink carrier aggregationfor the communication link of FIG. 2A.

FIG. 16A is a schematic diagram of one embodiment of a radio frequency(RF) communication system with a wireless communication device with afirst transmit duty cycle.

FIG. 16B is a schematic diagram of another embodiment of an RFcommunication system with a wireless communication device with secondtransmit duty cycle that is higher than the first transmit duty cycle.

FIG. 17A is a graph illustrating one example of an RF signal waveformversus time.

FIG. 17B is one example of a peak to average power ratio (PAPR)complementary cumulative distribution function (CCDF) for various cyclicprefix orthogonal frequency division multiplexing (CP-OFDM) waveformsrelative to a single carrier frequency division multiple access(SC-FDMA) reference waveform.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Acoustic wave filters can filter radio frequency (RF) signals in avariety of applications, such as in an RF front end of a mobile phone.An acoustic wave filter can be implemented with surface acoustic wave(SAW) devices. SAW devices include SAW resonators, SAW delay lines, andmulti-mode SAW (MMS) filters (e.g., double mode SAW (DMS) filters).

Acoustic wave filters can include SAW resonators that include amulti-layer piezoelectric substrate. Multi-layer piezoelectricsubstrates can provide good thermal dissipation characteristics andimproved temperature coefficient of frequency (TCF) relative to certainsingle layer piezoelectric substrates. For example, a SAW device with apiezoelectric layer on a high impedance support substrate, such assilicon, can achieve better temperature coefficient of frequency (TCF)and thermal dissipation compared to a similar device without the highimpedance support substrate.

For example, a SAW device can include a temperature compensation layer(e.g., a silicon dioxide (SiO₂) layer), a piezoelectric layer (e.g., alithium niobate (LN) layer), an interdigital transducer (IDT) electrodeover the piezoelectric layer, and a high impedance support substrate(e.g., a silicon substrate) under the piezoelectric layer. Such deviceswith the high impedance substrate under the piezoelectric layer canobtain a better TCF and/or a better thermal dissipation characteristicthan temperature compensated (TC) SAW devices that do not include thehigh impedance substrate structure in certain applications. However, SAWdevices that include a piezoelectric layer on certain high impedancesupport substrates can experience spurious responses as a result of backreflection from the high impedance support substrate. This can degrade afrequency response of a filter that includes the SAW devices.

In order to reduce and/or mitigate this degradation of the SAW deviceperformance, SAW devices can include a ceramic substrate, such as apolycrystalline spinel support substrate. A polycrystalline spinelsupport substrate can be a magnesium aluminate (MgAl₂O₄) spinelsubstrate. A polycrystalline spinel support substrate can scatter backreflections by a beam scattering feature of the polycrystalline spinelsubstrate. The polycrystalline spinel substrate can have desirableflatness characteristics. At least because the polycrystalline spinelsubstrate can have a desirable flatness, the polycrystalline spinelsubstrate can be directly bonded to a piezoelectric layer without anintervening adhesive. Such direct bonding can be a relatively easymanufacturing operation. The polycrystalline spinel substrate can alsoachieve advantages of other high impedance support substrates, such asimproved TCF and/or desirable thermal dissipation. However, apolycrystalline spinel substrate has a relatively low heat conductivity.Hence, the SAW device with a polycrystalline spinel substrate maygenerate a relatively high temperature, which can degrade theperformance of the SAW device.

Aspects of the present disclosure relate to SAW devices that include asupporting substrate (e.g., a single crystal layer), a ceramic layer(e.g., a spinel layer, such as a polycrystalline spinel layer) over thesupporting substrate, a piezoelectric layer (e.g., a lithium niobate(LN) layer) over the ceramic layer, an interdigital transducer (IDT)electrode over the piezoelectric layer. Such SAW devices can alsoinclude a temperature compensation layer (e.g., silicon dioxide (SiO2)layer) over the IDT electrode in certain embodiments. The SAW devicescan also include an adhesive layer disposed between the supportingsubstrate and the spinel layer in some applications.

SAW devices disclosed herein that include a polycrystalline spinel layerand a support substrate can achieve desirable suppression ofbackscattering and desirable heat dissipation. For example, temperaturesimulations indicate that chip temperature is decreased in a SAWresonator with a polycrystalline spinel layer on a silicon supportsubstrate compared with a similar SAW resonator with polycrystallinespinel as the base substrate. The polycrystalline spinel can alsoscatter elastic waves to suppress reflection of such elastic waves.

Although embodiments may be discussed with reference to SAW resonators,any suitable principles and advantages discussed herein can be appliedto any suitable SAW device and/or any other suitable acoustic wavedevice. Embodiments will now be discussed with reference to drawings.Any suitable combination of features of the embodiments disclosed hereincan be implemented together with each other.

FIG. 1 illustrates a cross section of a surface acoustic wave (SAW)resonator 1 according to an embodiment. The illustrated SAW resonator 1includes a piezoelectric layer 10, an IDT electrode 12 over thepiezoelectric layer 10, a temperature compensation layer 14 over the IDTelectrode 12, a ceramic layer (e.g., a polycrystalline spinel substrate16) below the piezoelectric layer 10, and a support substrate 22 belowthe polycrystalline substrate 16. The piezoelectric layer 10 can be anysuitable piezoelectric layer. In some embodiments, the piezoelectriclayer 10 can be a lithium based piezoelectric, such as a lithium niobate(LN) layer or a lithium tantalate (LT) layer. The temperaturecompensation layer 14 may include any suitable temperature compensationmaterial that has a positive temperature coefficient of frequency. Forinstance, the temperature compensation layer 14 can be a silicon dioxide(SiO₂) layer, a tellurium dioxide (TeO₂) layer or a silicon oxyfluoride(SiOF) layer in certain applications. A temperature compensation layercan include any suitable combination of SiO₂, TeO₂, and/or SiOF. In someembodiments, for example, as illustrated in FIGS. 2A and 5 , thetemperature compensation layer 14 of FIG. 1 may be omitted.

The polycrystalline spinel substrate 16 can be a magnesium aluminate(MgAl₂O₄) spinel substrate. The polycrystalline spinel substrate 16 canbe replaced with any suitable ceramic substrate. A ceramic substrate caninclude, for example, polycrystalline spinel (e.g., MgAl₂O₄), co-firedceramic, or polycrystalline aluminum nitride (AlN). The ceramicsubstrate can have higher acoustic impedance than an acoustic impedanceof the piezoelectric layer 10. The ceramic layer can be arranged toscatter back reflections of an acoustic wave generated by the SAWresonator 1.

Ceramics, such as polycrystalline spinel, are better wave scatteringmaterials than various single crystals. Accordingly, a ceramicsubstrate, such as the polycrystalline spinel substrate 16, can scatterwaves at a diffraction boundary between the polycrystalline spinel layer16 and the piezoelectric layer 10 of the surface acoustic wave device 1.With the back scattering of the polycrystalline spinel layer 16,spurious modes resulting from back scattering can be suppressed. Thiscan avoid and/or mitigate degradation of a frequency response of afilter that includes the SAW resonator 1.

The polycrystalline spinel substrate 16 can have desirable flatness atthe diffraction boundary between the polycrystalline spinel layer 16 andthe piezoelectric layer 10 (e.g., an upper surface 16 a of thepolycrystalline spinel layer 16). The polycrystalline spinel substrate16 can achieve desirable diffraction while being relatively smooth. Forinstance, the polycrystalline spinel layer 16 can have a smoothness in arange from about 0.1 nanometer (nm) to 2 nm. This is unlike some otherhigh impedance support substrates that can create spurious responses asa result of back reflection when they are relatively smooth. Thepolycrystalline spinel layer 16 can be bonded to the piezoelectric layer10. The polycrystalline spinel substrate 16 can be directly bonded tothe piezoelectric layer 10 without an intervening adhesive. There can belittle or no delamination of the polycrystalline spinel layer 16 and thepiezoelectric layer 10 after bonding.

The polycrystalline spinel layer 16 has a thickness T4. The thickness T4of the polycrystalline spinel layer 16 can be any suitable thickness.The thickness T4 of the polycrystalline spinel layer 16 can besufficiently thick to maintain structural integrity of a surfaceacoustic wave device. The thickness T4 can be determined in accordancewith principles and advantages explained with respect to FIG. 3 .

The support substrate 22 has a greater heat conductivity than thepolycrystalline spinel layer 16. For example, the support substrate 22can have a thermal conductivity that is at least 9 times the thermalconductivity of the polycrystalline spinel layer 16. The surfaceacoustic wave resonator 1 with the support substrate 22 that has agreater thermal conductivity than the polycrystalline spinel layer 16can be more durable than a similar surface acoustic wave resonator witha support substrate that does not have a greater thermal conductivitythan a polycrystalline spinel layer.

The support substrate 22 can be a single crystal layer. The supportsubstrate 22 can include, for example, silicon (Si), sapphire, aluminumoxide (Al₂O₃), aluminum nitride (AlN), quartz, glass with a relativelyhigh thermal conductivity, etc. In certain embodiments, the supportsubstrate 22 is a silicon substrate. The support substrate 22 has alower line expansion than the polycrystalline spinel layer 16 in certainapplications. In such applications, temperature coefficient of frequency(TCF) may be improved. In certain embodiments, the support substrate 22has a lower permittivity than the polycrystalline spinel layer 16. Insuch embodiments, the support substrate 22 may be highly isolated.

The support substrate 22 has a thickness T5. The thickness T5 of thesupport substrate 22 can be any suitable thickness. In some embodiments,the thickness T5 of the support substrate 22 can be greater than thethickness T4 of the polycrystalline spinel layer 16. The thickness T5can be determined, for example, as explained with respect to FIG. 3 .

The IDT electrode 12 illustrated in FIG. 1 includes a plurality of metallayers. The IDT electrode 12 can include a molybdenum (Mo) layer 18 andan aluminum (Al) layer 20. The IDT electrode 12 may include othermetals, such as, copper (Cu), Magnesium (Mg), titanium (Ti), tungsten(W), etc. The IDT electrode 12 may include alloys, such as AlMgCu, AlCu,etc. The polycrystalline spinel layer 16 can reduce the back reflectioncompared to other support substrates, such as a silicon substrate, asapphire substrate, or the like.

The Mo layer 18 of the IDT electrode 12 has a thickness T3. In someembodiments, the thickness T3 of the Mo layer 18 can be about 0.05L. Forexample, when the wavelength L is 4 micrometers (μm), the thickness T3of the Mo layer 18 can be 200 nm in such embodiments.

The piezoelectric layer 10 has a thickness T1. The thickness T1 of thepiezoelectric layer 10 can be selected based on a wavelength λ or L of asurface acoustic wave generated by the surface acoustic wave resonator1. The IDT electrode 12 has a pitch that sets the wavelength λ or L ofthe surface acoustic wave device 1. The piezoelectric layer 10 can besufficiently thick to avoid significant frequency variation. A thicknessT1 of the piezoelectric layer 10 of at least 3L can be sufficientlythick to mitigation frequency variation due to a relatively thinpiezoelectric layer 10. The thickness T1 of the piezoelectric layer 10can be in a range from, for example, 3L to 40L. As another example, thethickness T1 of the piezoelectric layer 10 can be in a range from 3L to20L. In some instances, the thickness T1 of the piezoelectric layer 10can be at least 5L, such as in a range from 5L to 40L. The wavelength Lof the surface acoustic wave can be, for example, 4 μm and the thicknessT1 of the piezoelectric layer 10 can be, for example, 20 μm, in someembodiments. As noted above, the piezoelectric layer 10 may include anysuitable piezoelectric layer, such as a lithium niobate (LN) layer or alithium tantalate (LT) layer.

The temperature compensation layer 14 can bring the TCF of the surfaceacoustic wave resonator 1 closer to zero to thereby provide temperaturecompensation. The temperature compensation layer 14 can improve theelectromechanical coupling coefficient k² of the SAW resonator 1relative to a similar SAW resonator without the temperature compensationlayer 14. This advantage of the temperature compensation layer 14 can bemore pronounced when the piezoelectric layer 10 is an LN layer. Thetemperature compensation layer 14 has a thickness T2. In someembodiments, the thickness T2 of the temperature compensation layer 14can be in a range from 0.1L to 0.5L. For example, when the wavelength Lis 4 μm, the thickness T2 of the temperature compensation layer 14 canbe 1200 nm.

In some embodiments, the thickness T1 of the piezoelectric layer 10 maybe adjusted by grinding from an upper surface 10 a of the piezoelectriclayer 10 after bonding a lower surface 10 b of the piezoelectric layer10 and an upper surface 16 a the polycrystalline spinel layer 16. Thepiezoelectric layer 10 and the polycrystalline spinel layer 16 can bedirectly bonded without an intervening adhesive. The lower surface 10 bof the piezoelectric layer 10 and the upper surface 16 a thepolycrystalline spinel layer 16 can be subjected to an appropriatepreparation for such direct bonding. The preparation of the surfaces 10b and 16 a can include smoothing the surfaces 10 b and/or 16 a, forexample, as discussed with reference to FIG. 6 . The temperaturecompensation layer 14 can be formed over the upper surface 10 a of thepiezoelectric layer 10.

FIG. 2A illustrates a cross section of a surface acoustic wave resonator2 that includes a polycrystalline spinel layer 16 according to anotherembodiment. The illustrated SAW resonator 2 includes a piezoelectriclayer 10, IDT electrode 12′ over the piezoelectric layer 10, a ceramiclayer (e.g., a polycrystalline spinel layer 16), and a support substrate22. Unless otherwise noted, elements shown in FIG. 2A may be the same asor generally similar to like numbered elements in FIG. 1 . The surfaceacoustic wave resonator 2 is like the surface acoustic wave resonator 1of FIG. 1 . However, unlike that the SAW resonator 1 illustrated in FIG.1 , the SAW resonator 2 does not include the temperature compensationlayer 14. The back scattering of the polycrystalline spinel layer 16 maybe unaffected by the absence of the temperature compensation layer 14 ofthe SAW resonator 1 illustrated in FIG. 1 . Also, the IDT electrode 12′illustrated in FIG. 2A is a single layer IDT. In some other embodiments,a multi-layer IDT (e.g., the IDT electrode 12 illustrated in FIG. 1 )that include two or more layers can be used.

FIG. 2B is a simulated heat map of a SAW chip that includes the SAWresonator 2 of FIG. 2A. For this simulation, a lithium niobate (LN)layer is used for the piezoelectric layer 10, and a silicon (Si)substrate is used for the support substrate 22. The SAW resonator usedin the thermal simulation has a thickness T1 of the piezoelectric layerof 20 μm, a thickness T4 of the polycrystalline spinel layer of 20 μm,and a thickness T5 of a silicon support substrate of 120 μm. From thethermal simulation result of the SAW chip that includes the SAWresonator, as seen from the top of the simulated heat map, highertemperature is indicated towards the right hand side on FIG. 2B comparedto the left hand side. The maximum chip temperature observed from thethermal simulation is 39° C. This is a relatively low temperature as themaximum temperature for a SAW chip. The maximum SAW chip temperaturewith SAW resonators 2 of FIG. 2A was simulated to be more than 10° C.lower that a similar SAW chip with resonators that included apolycrystalline base substrate without a silicon support substrate. Thisreduction in maximum SAW chip temperature can be due to the thermalconductivity of the support substrate 22. Therefore, the SAW resonator 2can provide a good heat dissipation. Such heat dissipation can beachieved while also suppressing spurious modes resulting from backscattering.

FIG. 3 is a graph of a thermal simulation result of the SAW resonator 2used in the simulation of FIG. 2B for varying thicknesses of thepolycrystalline spinel layer 16. The total thickness of thepolycrystalline spinel layer 16 and the support substrate 22 (T4+T5) isset to be 140 μm. The x-axis shows the thickness T4 of thepolycrystalline spinel layer 16 ranging from 0 to 140 μm, and the y-axisshows the maximum temperature of the SAW resonator 2 in operation.Therefore, when the thickness T4 of the polycrystalline spinel layer 16is, for example, 50 μm, the thickness T5 of the support substrate 22 is90 μm, and the maximum temperature for the simulated embodiment of theSAW resonator 2 is about 42.5° C.

The lower end of the range of thickness T4 of the polycrystalline spinellayer 16 can be determined based at least in part on back reflectionsuppression properties of the polycrystalline spinel layer 16. Forexample, the thickness T4 can be at least about 1L, or 4 μm when thewavelength L is 4 μm. At a thickness T4 of about 1L, the polycrystallinespinel layer 16 can provide sufficient backscattering for performance ofa SAW resonator in certain applications. The upper end of the thicknessT4 of the polycrystalline spinel layer 16 can be determined based atleast in part on the maximum device thickness (140 μm in this case),and/or the desired maximum temperature of the SAW chip. For example, ifa maximum desired temperate of a SAW chip is 45° C., the thickness T4 ofthe polycrystalline spinel layer 16 can be selected to be less thanabout 80 μm based on FIG. 3 .

In certain applications, a range of the thickness T4 of thepolycrystalline spinel layer 16 can be chosen based at least in part onan inflection point observed within the range between the lower end andthe upper end of the thickness T4. For example, on the curve shown inthe graph in FIG. 3 , there is an inflection point at around T4=75 μm.Therefore, the thickness T4 of the polycrystalline spinel layer 16 canbe selected to be in a range from 1L to about 75 μm in certainembodiments.

FIG. 4 illustrates a cross section of a surface acoustic wave resonator3 according to an embodiment. The illustrated SAW resonator 3 includes apiezoelectric layer 10 (e.g., a lithium niobate (LN) layer, a lithiumtantalate (LT) layer, etc.), an IDT electrode 12 over the piezoelectriclayer 10, a temperature compensation layer 14 over the IDT electrode 12,a ceramic layer (e.g., a polycrystalline spinel layer 16) below thepiezoelectric layer 10, a support substrate 22 below the polycrystallinesubstrate 16, and an adhesive layer 24 between the polycrystallinespinel layer 16 and the support substrate 22. Unless otherwise noted,elements shown in FIG. 4 may be the same as or generally similar to likenumbered elements in FIGS. 1 and 2A.

The adhesive layer 24 can be any suitable material that provides abetter adhesion between the polycrystalline spinel layer 16 and thesupport substrate 22 than without the adhesive layer 24. It may bebeneficial to use a material that has a relatively high thermalconductivity for the adhesive layer 24. The thermal conductivity of theadhesive layer 24 can be greater than the thermal conductivity of thepolycrystalline spinel layer 16. In certain embodiments, the adhesivelayer 24 can include aluminum (Al), titanium (Ti), a nitride, etc. Theadhesive layer 24 can mitigate and/or reduce the chance of delaminationbetween the polycrystalline layer substrate 16 and the support substrate22, and/or provide a good thermal conductivity.

FIG. 5 illustrates a cross section of a surface acoustic wave resonator4 according to an embodiment. The illustrated SAW resonator 4 includes apiezoelectric layer 10, an IDT electrode 12 over the piezoelectric layer10, a polycrystalline spinel layer 16 below the piezoelectric layer 10,and a support substrate 22 below the polycrystalline layer 16. Unlessotherwise noted, elements shown in FIG. 5 may be the same as orgenerally similar to like numbered elements in FIGS. 1, 2A and 4 .

Unlike the embodiment shown in FIG. 1 , the SAW resonator 4 illustratedin FIG. 5 does not include the temperature compensation layer 14illustrated in FIG. 1 . Such embodiments that do not include thetemperature compensation layer 14 can be more preferable when thepiezoelectric layer is a lithium tantalate (LT) layer than when thepiezoelectric layer is a lithium niobate (LN) layer.

FIG. 6A is a flow chart that illustrates a manufacturing process 6 offorming a SAW device according to an embodiment. The manufacturingprocess 6 will now be discussed referring to the SAW resonator 1illustrated in FIG. 1 and/or another embodiment as an example. Anysuitable principles and advantages of the process 6 can be used tomanufacture any SAW resonator disclosed herein. The manufacturingprocess 6 can be used to fabricate any suitable SAW device with apolycrystalline spinel layer. The operations of the manufacturingprocess 6 can be performed in any suitable order. For example, one ormore of operations illustrated in FIG. 6A may be performed in adifferent order or sequence than illustrated as suitable.

The manufacturing process 6 includes a preparing operation 30 ofpreparing a surface of a polycrystalline spinel layer and/or a supportsubstrate for attaching (e.g., bonding). A lower surface 16 b of thepolycrystalline spinel layer 16 and/or an upper surface 22 a of thesupport substrate 22 of the SAW resonator 1 can be prepared for directbonding. The preparation can include smoothing the surfaces 16 b and/or22 a by way of, for example, chemical-mechanical polishing (CMP). Forinstance, the upper surface 22 a of the support substrate 22 can besmoothed by CMP. In some embodiments, the upper surface 22 a of thesupport substrate 22 can be smoothed so as to have a maximum surfaceroughness of about 2 nm or less. In such embodiments, the surfaceroughness of the upper surface 22 a can have an average surfaceroughness of about 1 nm or less. The minimum surface roughness of theupper surface 22 a of the support substrate 22 can be about 0.1 nm insuch embodiments. Accordingly, the preparing operation 30 can involvesmoothing the upper surface 22 a of the support substrate 22 to asurface roughness in a range from 0.1 nm to 2 nm. The preparationoperation 30 may be performed at the wafer level. In certain instances,surfaces of polycrystalline spinel layers of different SAW resonators ona same wafer can have different surface roughness.

The manufacturing process 6 also includes an attaching operation 32 ofattaching a polycrystalline spinel layer to a support substrate. Theattaching can involve bonding. For instance, the lower surface 16 b ofthe polycrystalline spinel layer 16 and the upper surface 22 a of thesupport substrate 22 of the SAW resonator 1 can be bonded together. Whenthe surfaces 16 b and/or 22 a are prepared for direct bonding, asexplained above, the polycrystalline spinel layer 16 and the supportsubstrate 22 can be directly bonded without an intervening adhesive. Thesurfaces 16 b and/or 22 a of the SAW resonator 10 can be directly bondedto each other by contact without applying an external pressure and/orheat.

The attaching operation 32 can include attaching the lower surface 16 bof the polycrystalline spinel layer 16 and the upper surface 22 a of thesupport substrate 22 by way of an adhesive layer 24 illustrated in FIG.4 . In such embodiments, the preparing operation may include,alternatively or in addition, applying the adhesive layer 24 on one ofthe lower surface 16 b of the polycrystalline spinel layer 16 or theupper surface 22 a of the support substrate 22.

The manufacturing process 6 also includes another preparing operation 34of preparing a surface of a piezoelectric layer and/or a polycrystallinespinel layer for bonding. The lower surface 10 b of the piezoelectriclayer 10 and/or the upper surface 16 a of the polycrystalline spinellayer 16 of the SAW resonator 1 can be prepared for direct bonding. Thepreparation can include smoothing the surfaces 10 b and/or 16 a by wayof, for example, chemical-mechanical polishing (CMP). For instance, theupper surface 16 a of the polycrystalline spinel layer 16 can besmoothed by CMP. In some embodiments, the upper surface 16 a of thepolycrystalline spinel layer 16 can be smoothed so as to have a maximumsurface roughness of about 2 nm or less. In such embodiments, thesurface roughness of the upper surface 16 a can have an average surfaceroughness of about 1 m or less. The minimum surface roughness of theupper surface 16 a of the polycrystalline spinel layer 16 can be about0.1 nm in such embodiments. Accordingly, the preparing operation 34 caninvolve smoothing the upper surface 16 a of the polycrystalline spinellayer 16 to a surface roughness in a range from 0.1 nm to 2 nm. Thepreparation operation 34 may be performed at the wafer level. In certaininstances, surfaces of polycrystalline spinel layers of different SAWresonators on a same wafer can have different surface roughness.

The manufacturing process 6 also includes a bonding operation 36 ofbonding a polycrystalline spinel layer to a piezoelectric layer. Forinstance, the lower surface 10 b of the piezoelectric layer 10 and theupper surface 16 a of the polycrystalline spinel layer 16 can be bondedtogether. When the surfaces 10 b, 16 a are prepared for direct bonding,as explained above, the piezoelectric layer 10 and the polycrystallinespinel layer 16 can be bonded without an intervening adhesive. Thesurfaces 10 b and 16 a of the SAW resonator 1 can be directly bonded toeach other by contact without applying an external pressure and/or heat.

The manufacturing process 6 further includes an interdigital transducer(IDT) electrode forming operation 38 of forming an IDT electrode over apiezoelectric layer. The IDT electrode 12 is typically formed on theupper surface 10 a of the piezoelectric layer 10 prior to forming thetemperature compensation layer 14. The IDT electrode 12 can be formedby, for example, forming the Mo layer 18 over the piezoelectric layer 10and forming the Al layer 20 over the Mo layer 18.

The manufacturing process 6 can also include a temperature compensationlayer forming operation 39 of forming a temperature compensation layerover a piezoelectric layer and an IDT electrode. With a temperaturecompensation layer over a piezoelectric layer, a SAW resonator can bereferred to as a temperature compensated SAW (TC-SAW) resonator. Thetemperature compensation layer 14 may be formed by, for example,depositing a temperature compensation material (e.g., SiO₂) over thepiezoelectric layer 10 and the IDT electrode 12. The formation of thetemperature compensation layer 14 can control the thickness T2 of thetemperature compensation layer 14. For example, temperature compensationmaterial can be deposited to have the thickness T2 in a range from 0.3Lto 0.5L in which L is the wave length of a surface acoustic wavegenerated by the SAW resonator.

FIG. 6B is a flow chart that illustrates another manufacturing process 7of forming a SAW resonator according to an embodiment. The manufacturingprocess 7 can be generally similar to the manufacturing process 6illustrated in FIG. 6A applied to a ceramic layer. The operations of themanufacturing process 7 can be performed in any suitable order. Forexample, one or more of operations illustrated in FIG. 6B may beperformed in a different order or sequence than illustrated as suitable.

The manufacturing process 7 includes a preparing operation 30′ ofpreparing a surface of a ceramic layer and/or a support substrate forattaching (e.g., bonding). The manufacturing process 7 also includes anattaching operation 32′ (e.g., a bonding operation) of attaching aceramic layer to a support substrate. The manufacturing process 7 alsoincludes another preparing operation 34′ of preparing a surface of apiezoelectric layer and/or a ceramic layer for bonding. Themanufacturing process 7 also includes a bonding operation 36′ of bondinga ceramic layer to a piezoelectric layer. The manufacturing process 7further includes an interdigital transducer (IDT) electrode formingoperation 38 of forming an IDT electrode over a piezoelectric layer. Themanufacturing process 7 can also include a temperature compensationlayer forming operation 39 of forming a temperature compensation layerover a piezoelectric layer and an IDT electrode.

A filter can filter a radio frequency signal. The filter can include anyone or more acoustic wave devices disclosed herein. For example, amethod of manufacturing a surface acoustic wave filter can includeattaching a support substrate to a ceramic layer. The support substratehas a higher thermal conductivity than the ceramic layer. The supportsubstrate can be a single crystal substrate, such as a siliconsubstrate. The ceramic layer can be a polycrystalline spinel layer. Themethod can also include bonding a piezoelectric layer to a surface ofthe ceramic layer. The method can also include forming an interdigitaltransducer (IDT) electrode over the piezoelectric layer. The supportsubstrate, the ceramic layer, the piezoelectric layer, and theinterdigital transducer electrode can define a SAW resonator. The methodcan further include forming a temperature compensation layer over theIDT electrode. The method can further include electrically connectingthe surface acoustic wave resonator to another surface acoustic waveresonator of the surface acoustic wave filter. The method can furtherinclude electrically connecting the surface acoustic wave resonator to aplurality of other surface acoustic wave resonators of the surfaceacoustic wave filter.

FIGS. 7A-7D illustrate cross sections of a SAW resonator at varioussteps in a manufacturing process, according to embodiment. Any suitableprinciples and advantages of the process illustrated in FIGS. 7A-7D canbe used to manufacture any suitable SAW resonator and/or any suitableacoustic wave device disclosed herein. The manufacturing processillustrated in FIGS. 7A-7D can be used to fabricate any suitable SAWdevice with a polycrystalline spinel layer and/or any other suitableceramic layer. The steps of the manufacturing process illustrated inFIGS. 7A-7D can be performed in any suitable order. For example, one ormore of operations illustrated in FIGS. 7A-7D may be performed in adifferent order or sequence than illustrated as suitable. Acoustic wavedevices in accordance with principles and advantages disclosed hereincan be manufactured using some or all of the steps of the manufacturingprocess disclosed with reference to FIGS. 7A-7D. Although themanufacturing process associated with FIGS. 7A-7D may be described withreference to a polycrystalline spinel layer, any suitable combination offeatures of the manufacturing process can be applied to manufacturingany other suitable ceramic substrate.

In FIG. 7A a lower surface 16 b of a polycrystalline spinel layer 16 andan upper surface 22 a of a support substrate 22 are attached. In someembodiments, the polycrystalline spinel layer 16 and the supportsubstrate 22 can be directly bonded to each other. In some otherembodiments, the polycrystalline spinel layer 16 and the supportsubstrate 22 can be bonded by way of an intervening adhesive.

In FIG. 7B, a lower surface 10 b of a piezoelectric layer 10 and anupper surface 16 a of the polycrystalline spinel layer 16 are bonded. Insome embodiments, the piezoelectric layer 10 and the polycrystallinespinel layer 16 can be directly bonded to each other. In some otherembodiments, the piezoelectric layer 10 and the polycrystalline spinellayer 16 can be bonded by way of an intervening adhesive.

In FIG. 7C, an interdigital transducer (IDT) electrode 12 is formed onan upper surface 10 a of the piezoelectric layer 10. The IDT electrode12 can be formed by, for example, forming the Mo layer 18 over thepiezoelectric layer 10 and forming the Al layer 20 over the Mo layer 18.

In FIG. 7D, a temperature compensation layer 14 is formed over thepiezoelectric layer 10 and the IDT electrode 12. The temperaturecompensation layer 14 may be formed by, for example, depositing atemperature compensation material (e.g., SiO₂) over the piezoelectriclayer 10 and the IDT electrode 12.

FIG. 8A is a schematic diagram of an example transmit filter 45 thatincludes surface acoustic wave resonators of a surface acoustic wavecomponent according to an embodiment. The transmit filter 45 can be aband pass filter. The illustrated transmit filter 45 is arranged tofilter a radio frequency signal received at a transmit port TX andprovide a filtered output signal to an antenna port ANT. The transmitfilter 45 includes series SAW resonators TS1, TS2, TS3, TS4, TS5, TS6,and TS7, shunt SAW resonators TP1, TP2, TP3, TP4, and TP5, series inputinductor L1, and shunt inductor L2. Some or all of the SAW resonatorsTS1, TS2, TS3, TS4, TS5, TS6, and TS7 and/or TP1, TP2, TP3, TP4, and TP5can be a SAW resonators with a polycrystalline spinel layer over asupport substrate in accordance with any suitable principles andadvantages disclosed herein. For instance, one or more of the SAWresonators of the transmit filter 45 can be a surface acoustic waveresonator 1 of FIG. 1 . Alternatively or additionally, one or more ofthe SAW resonators of the transmit filter 45 can be any surface acousticwave resonator disclosed herein. Any suitable number of series SAWresonators and shunt SAW resonators can be included in a transmit filter45.

FIG. 8B is a schematic diagram of a receive filter 50 that includessurface acoustic wave resonators of a surface acoustic wave componentaccording to an embodiment. The receive filter 50 can be a band passfilter. The illustrated receive filter 50 is arranged to filter a radiofrequency signal received at an antenna port ANT and provide a filteredoutput signal to a receive port RX. The receive filter 50 includesseries SAW resonators RS1, RS2, RS3, RS4, RS5, RS6, RS7, and RS8, shuntSAW resonators RP1, RP2, RP3, RP4, RP5, and RP6, shunt inductor L2, andseries output inductor L3. Some or all of the SAW resonators RS1, RS2,RS3, RS4, RS5, RS6, RS7, and RS8 and/or RP1, RP2, RP3, RP4, RP5, and RP6can be SAW resonators with a polycrystalline spinel layer over a supportsubstrate in accordance with any suitable principles and advantagesdisclosed herein. For instance, one or more of the SAW resonators of thereceive filter 50 can be a surface acoustic wave resonator 1 of FIG. 1 .Alternatively or additionally, one or more of the SAW resonators of thereceive filter 50 can be any surface acoustic wave resonator disclosedherein. Any suitable number of series SAW resonators and shunt SAWresonators can be included in a receive filter 50.

FIG. 9 is a schematic diagram of a radio frequency module 75 thatincludes a surface acoustic wave component 76 according to anembodiment. The illustrated radio frequency module 75 includes the SAWcomponent 76 and other circuitry 77. The SAW component 76 can includeone or more SAW resonators and/or other acoustic wave devices with anysuitable combination of features of the SAW resonators disclosed herein.The SAW component 76 can include a SAW die that includes SAW resonators.

The SAW component 76 shown in FIG. 9 includes a filter 78 and terminals79A and 79B. The filter 78 includes SAW resonators. One or more of theSAW resonators can be implemented in accordance with any suitableprinciples and advantages of the surface acoustic wave resonator 1 ofFIG. 1 and/or any surface acoustic wave resonator disclosed herein. Thefilter 78 can be a TC-SAW filter arranged as a band pass filter tofilter radio frequency signals with frequencies below about 3.5 GHz incertain applications. The terminals 79A and 78B can serve, for example,as an input contact and an output contact. The SAW component 76 and theother circuitry 77 are on a common packaging substrate 80 in FIG. 9 .The package substrate 80 can be a laminate substrate. The terminals 79Aand 79B can be electrically connected to contacts 81A and 81B,respectively, on the packaging substrate 80 by way of electricalconnectors 82A and 82B, respectively. The electrical connectors 82A and82B can be bumps or wire bonds, for example. The other circuitry 77 caninclude any suitable additional circuitry. For example, the othercircuitry can include one or more one or more power amplifiers, one ormore radio frequency switches, one or more additional filters, one ormore low noise amplifiers, the like, or any suitable combinationthereof. The radio frequency module 75 can include one or more packagingstructures to, for example, provide protection and/or facilitate easierhandling of the radio frequency module 75. Such a packaging structurecan include an overmold structure formed over the packaging substrate75. The overmold structure can encapsulate some or all of the componentsof the radio frequency module 75.

FIG. 10 is a schematic diagram of a radio frequency module 84 thatincludes a surface acoustic wave component according to an embodiment.As illustrated, the radio frequency module 84 includes duplexers 85A to85N that include respective transmit filters 86A1 to 86N1 and respectivereceive filters 86A2 to 86N2, a power amplifier 87, a select switch 88,and an antenna switch 89. In some instances, the module 84 can includeone or more low noise amplifiers configured to receive a signal from oneor more receive filters of the receive filters 86A2 to 86N2. The radiofrequency module 84 can include a package that encloses the illustratedelements. The illustrated elements can be disposed on a common packagingsubstrate 80. The packaging substrate can be a laminate substrate, forexample.

The duplexers 85A to 85N can each include two acoustic wave filterscoupled to a common node. The two acoustic wave filters can be atransmit filter and a receive filter. As illustrated, the transmitfilter and the receive filter can each be band pass filters arranged tofilter a radio frequency signal. One or more of the transmit filters86A1 to 86N1 can include one or more SAW resonators in accordance withany suitable principles and advantages disclosed herein. Similarly, oneor more of the receive filters 86A2 to 86N2 can include one or more SAWresonators in accordance with any suitable principles and advantagesdisclosed herein. Although FIG. 10 illustrates duplexers, any suitableprinciples and advantages disclosed herein can be implemented in othermultiplexers (e.g., quadplexers, hexaplexers, octoplexers, etc.) and/orin switch-plexers. Such multiplexers can include multiplexers with fixedmultiplexing, multiplexers with switched multiplexing, or multiplexerswith a combination of switched multiplexing and fixed multiplexing.

The power amplifier 87 can amplify a radio frequency signal. Theillustrated switch 88 is a multi-throw radio frequency switch. Theswitch 88 can electrically couple an output of the power amplifier 87 toa selected transmit filter of the transmit filters 86A1 to 86N1. In someinstances, the switch 88 can electrically connect the output of thepower amplifier 87 to more than one of the transmit filters 86A1 to86N1. The antenna switch 89 can selectively couple a signal from one ormore of the duplexers 85A to 85N to an antenna port ANT. The duplexers85A to 85N can be associated with different frequency bands and/ordifferent modes of operation (e.g., different power modes, differentsignaling modes, etc.).

FIG. 11 is a schematic block diagram of a module 90 that includesduplexers 91A to 91N and an antenna switch 92. One or more filters ofthe duplexers 91A to 91N can include any suitable number of surfaceacoustic wave resonators in accordance with any suitable principles andadvantages discussed herein. Any suitable number of duplexers 91A to 91Ncan be implemented. The antenna switch 92 can have a number of throwscorresponding to the number of duplexers 91A to 91N. The antenna switch92 can electrically couple a selected duplexer to an antenna port of themodule 90.

FIG. 12A is a schematic block diagram of a module 110 that includes apower amplifier 112, a radio frequency switch 114, and duplexers 91A to91N in accordance with one or more embodiments. The power amplifier 112can amplify a radio frequency signal. The radio frequency switch 114 canbe a multi-throw radio frequency switch. The radio frequency switch 114can electrically couple an output of the power amplifier 112 to aselected transmit filter of the duplexers 91A to 91N. One or morefilters of the duplexers 91A to 91N can include any suitable number ofsurface acoustic wave resonators with a polycrystalline spinel layerover a support substrate in accordance with any suitable principles andadvantages discussed herein. Any suitable number of duplexers 91A to 91Ncan be implemented.

FIG. 12B is a schematic block diagram of a module 110′ that includesfilters 91A′ to 91N′, a radio frequency switch 114′, and a low noiseamplifier 115 according to an embodiment. One or more filters of thefilters 91A′ to 91N′ can include any suitable number of acoustic waveresonators in accordance with any suitable principles and advantagesdisclosed herein. Any suitable number of filters 91A′ to 91N′ can beimplemented. The illustrated filters 91A′ to 91N′ are receive filters.In some embodiments, one or more of the filters 91A′ to 91N′ can beincluded in a multiplexer that also includes a transmit filter. Theradio frequency switch 114′ can be a multi-throw radio frequency switch.The radio frequency switch 114′ can electrically couple an output of aselected filter of filters 91A′ to 91N′ to the low noise amplifier 115.In some embodiments (not illustrated), a plurality of low noiseamplifiers can be implemented. The module 110′ can include diversityreceive features in certain applications.

FIG. 13A is a schematic diagram of a wireless communication device 120that includes filters 123 in a radio frequency front end 122 accordingto an embodiment. The filters 123 can include one or more SAW resonatorsin accordance with any suitable principles and advantages discussedherein. The wireless communication device 120 can be any suitablewireless communication device. For instance, a wireless communicationdevice 120 can be a mobile phone, such as a smart phone. As illustrated,the wireless communication device 120 includes an antenna 121, an RFfront end 122, a transceiver 124, a processor 125, a memory 126, and auser interface 127. The antenna 121 can transmit/receive RF signalsprovided by the RF front end 122. Such RF signals can include carrieraggregation signals. Although not illustrated, the wirelesscommunication device 120 can include a microphone and a speaker incertain applications.

The RF front end 122 can include one or more power amplifiers, one ormore low noise amplifiers, one or more RF switches, one or more receivefilters, one or more transmit filters, one or more duplex filters, oneor more multiplexers, one or more frequency multiplexing circuits, thelike, or any suitable combination thereof. The RF front end 122 cantransmit and receive RF signals associated with any suitablecommunication standards. The filters 123 can include SAW resonators of aSAW component that includes any suitable combination of featuresdiscussed with reference to any embodiments discussed above.

The transceiver 124 can provide RF signals to the RF front end 122 foramplification and/or other processing. The transceiver 124 can alsoprocess an RF signal provided by a low noise amplifier of the RF frontend 122. The transceiver 124 is in communication with the processor 125.The processor 125 can be a baseband processor. The processor 125 canprovide any suitable base band processing functions for the wirelesscommunication device 120. The memory 126 can be accessed by theprocessor 125. The memory 126 can store any suitable data for thewireless communication device 120. The user interface 127 can be anysuitable user interface, such as a display with touch screencapabilities.

FIG. 13B is a schematic diagram of a wireless communication device 130that includes filters 123 in a radio frequency front end 122 and asecond filter 133 in a diversity receive module 132. The wirelesscommunication device 130 is like the wireless communication device 100of FIG. 13A, except that the wireless communication device 130 alsoincludes diversity receive features. As illustrated in FIG. 13B, thewireless communication device 130 includes a diversity antenna 131, adiversity module 132 configured to process signals received by thediversity antenna 131 and including filters 133, and a transceiver 134in communication with both the radio frequency front end 122 and thediversity receive module 132. The filters 133 can include one or moreSAW resonators that include any suitable combination of featuresdiscussed with reference to any embodiments discussed above.

Acoustic wave devices disclosed herein can be implemented in astandalone filter. Acoustic wave devices disclosed herein can beimplemented in one or more filters of multiplexer (e.g., a duplexer)with fixed multiplexing. Acoustic wave devices disclosed herein can beimplemented in one or more filters of multiplexer with switchedmultiplexing. Acoustic wave devices disclosed herein can be implementedin one or more filters of a multiplexer with a combination of fixedmultiplexing and switched multiplexing.

The 3rd Generation Partnership Project (3GPP) is a collaboration betweengroups of telecommunications standard bodies across the world. Thetechnical specifications controlled by 3GPP can be expanded and revisedby specification releases, which can span multiple years and specify abreadth of new features and evolutions. 3GPP introduced Phase 1 of fifthgeneration (5G) technology in Release 15, and plans to introduce Phase 2of 5G technology in Release 16 (targeted for 2020). Subsequent 3GPPreleases will further evolve and expand 5G technology. 5G technology isalso referred to herein as 5G New Radio (NR).

5G NR supports or plans to support a variety of features, such ascommunications over millimeter wave spectrum, beamforming capability,high spectral efficiency waveforms, low latency communications, multipleradio numerology, and/or non-orthogonal multiple access (NOMA). Althoughsuch RF functionalities offer flexibility to networks and enhance userdata rates, supporting such features can pose a number of technicalchallenges.

The teachings herein are applicable to a wide variety of communicationsystems, including, but not limited to, communication systems usingadvanced cellular technologies, such as LTE-Advanced, LTE-Advanced Pro,and/or 5G NR.

An acoustic wave device including any suitable combination of featuresdisclosed herein be included in a filter arranged to filter a radiofrequency signal in a fifth generation (5G) New Radio (NR) operatingband within Frequency Range 1 (FR1). A filter arranged to filter a radiofrequency signal in a 5G NR operating band can include one or more SAWdevices disclosed herein. FR1 can be from 410 MHz to 7.125 GHz, forexample, as specified in a current 5G NR specification. One or moreacoustic wave devices in accordance with any suitable principles andadvantages disclosed herein can be included in a filter arranged tofilter a radio frequency signal in a 4G LTE operating band and/or in afilter having a passband that includes a fourth generation (4G) LongTerm Evolution (LTE) operating band and a 5G NR operating band.

FIG. 14 is a schematic diagram of one example of a communication network140. The communication network 140 includes a macro cell base station141, a small cell base station 143, and various examples of userequipment (UE), including a first mobile device 142 a, awireless-connected car 142 b, a laptop 142 c, a stationary wirelessdevice 142 d, a wireless-connected train 142 e, a second mobile device142 f, and a third mobile device 142 g. One or more of the macro cellbase station 141, the small cell base station 143, or UEs illustrated inFIG. 14 can implement one or more of the acoustic wave devices (e.g.,SAW resonators) disclosed herein.

Although specific examples of base stations and user equipment areillustrated in FIG. 14 , a communication network can include basestations and user equipment of a wide variety of types and/or numbers.

For instance, in the example shown, the communication network 140includes the macro cell base station 141 and the small cell base station143. The small cell base station 143 can operate with relatively lowerpower, shorter range, and/or with fewer concurrent users relative to themacro cell base station 141. The small cell base station 143 can also bereferred to as a femtocell, a picocell, or a microcell. Although thecommunication network 140 is illustrated as including two base stations,the communication network 140 can be implemented to include more orfewer base stations and/or base stations of other types.

Although various examples of user equipment are shown, the teachingsherein are applicable to a wide variety of user equipment, including,but not limited to, mobile phones, tablets, laptops, Internet of Things(IoT) devices, wearable electronics, customer premises equipment (CPE),wireless-connected vehicles, wireless relays, and/or a wide variety ofother communication devices. Furthermore, user equipment includes notonly currently available communication devices that operate in acellular network, but also subsequently developed communication devicesthat will be readily implementable with the inventive systems,processes, methods, and devices as described and claimed herein.

The illustrated communication network 140 of FIG. 14 supportscommunications using a variety of cellular technologies, including, forexample, 4G LTE and 5G NR. In certain implementations, the communicationnetwork 140 is further adapted to provide a wireless local area network(WLAN), such as WiFi. Although various examples of communicationtechnologies have been provided, the communication network 140 can beadapted to support a wide variety of communication technologies.

Various communication links of the communication network 140 have beendepicted in FIG. 14 . The communication links can be duplexed in a widevariety of ways, including, for example, using frequency-divisionduplexing (FDD) and/or time-division duplexing (TDD). FDD is a type ofradio frequency communications that uses different frequencies fortransmitting and receiving signals. FDD can provide a number ofadvantages, such as high data rates and low latency. In contrast, TDD isa type of radio frequency communications that uses about the samefrequency for transmitting and receiving signals, and in which transmitand receive communications are switched in time. TDD can provide anumber of advantages, such as efficient use of spectrum and variableallocation of throughput between transmit and receive directions.

In certain implementations, user equipment can communicate with a basestation using one or more of 4G LTE, 5G NR, and WiFi technologies. Incertain implementations, enhanced license assisted access (eLAA) is usedto aggregate one or more licensed frequency carriers (for instance,licensed 4G LTE and/or 5G NR frequencies), with one or more unlicensedcarriers (for instance, unlicensed WiFi frequencies).

As shown in FIG. 14 , the communication links include not onlycommunication links between UE and base stations, but also UE to UEcommunications and base station to base station communications. Forexample, the communication network 140 can be implemented to supportself-fronthaul and/or self-backhaul (for instance, as between mobiledevice 142 g and mobile device 142 f).

The communication links can operate over a wide variety of frequencies.In certain implementations, communications are supported using 5G NRtechnology over one or more frequency bands that are less than 6Gigahertz (GHz) and/or over one or more frequency bands that are greaterthan 6 GHz. For example, the communication links can serve FrequencyRange 1 (FR1), Frequency Range 2 (FR2), or a combination thereof. Anacoustic wave filter including at least one acoustic wave devicedisclosed herein can filter a radio frequency signal within FR1. In oneembodiment, one or more of the mobile devices support a HPUE power classspecification.

In certain implementations, a base station and/or user equipmentcommunicates using beamforming. For example, beamforming can be used tofocus signal strength to overcome path losses, such as high lossassociated with communicating over high signal frequencies. In certainembodiments, user equipment, such as one or more mobile phones,communicate using beamforming on millimeter wave frequency bands in therange of 30 GHz to 300 GHz and/or upper centimeter wave frequencies inthe range of 6 GHz to 30 GHz, or more particularly, 24 GHz to 30 GHz.

Different users of the communication network 140 can share availablenetwork resources, such as available frequency spectrum, in a widevariety of ways. In one example, frequency division multiple access(FDMA) is used to divide a frequency band into multiple frequencycarriers. Additionally, one or more carriers are allocated to aparticular user. Examples of FDMA include, but are not limited to,single carrier FDMA (SC-FDMA) and orthogonal FDMA (OFDMA). OFDMA is amulticarrier technology that subdivides the available bandwidth intomultiple mutually orthogonal narrowband subcarriers, which can beseparately assigned to different users.

Other examples of shared access include, but are not limited to, timedivision multiple access (TDMA) in which a user is allocated particulartime slots for using a frequency resource, code division multiple access(CDMA) in which a frequency resource is shared amongst different usersby assigning each user a unique code, space-divisional multiple access(SDMA) in which beamforming is used to provide shared access by spatialdivision, and non-orthogonal multiple access (NOMA) in which the powerdomain is used for multiple access. For example, NOMA can be used toserve multiple users at the same frequency, time, and/or code, but withdifferent power levels.

Enhanced mobile broadband (eMBB) refers to technology for growing systemcapacity of LTE networks. For example, eMBB can refer to communicationswith a peak data rate of at least 10 Gbps and a minimum of 100 Mbps foreach user. Ultra-reliable low latency communications (uRLLC) refers totechnology for communication with very low latency, for instance, lessthan 2 milliseconds. uRLLC can be used for mission-criticalcommunications such as for autonomous driving and/or remote surgeryapplications. Massive machine-type communications (mMTC) refers to lowcost and low data rate communications associated with wirelessconnections to everyday objects, such as those associated with Internetof Things (IoT) applications.

The communication network 140 of FIG. 14 can be used to support a widevariety of advanced communication features, including, but not limitedto, eMBB, uRLLC, and/or mMTC.

Out of band rejection can be improved by suppressing back reflection byimplementing any suitable principles and advantages discussed herein.For example, a polycrystalline spinel substrate and/or any othersuitable ceramic substrate, implemented in accordance with any suitableprinciples and advantages disclosed herein can scatter back reflectionsby a beam scattering feature of the polycrystalline spinel substrate.This can improve out of band rejection. Reduced out of band rejectioncan be advantageous in various 5G NR applications, such as applicationsinvolving carrier aggregation. Example carrier aggregations will bediscussed with reference to FIGS. 15A to 15C. In carrier aggregationapplications, suppressing out of band rejection for a filter for acomponent carrier in a frequency range for another component carrier ofthe carrier aggregation can increase performance.

FIG. 15A is a schematic diagram of one example of a communication linkusing carrier aggregation. Carrier aggregation can be used to widenbandwidth of the communication link by supporting communications overmultiple frequency carriers, thereby increasing user data rates andenhancing network capacity by utilizing fragmented spectrum allocations.

In the illustrated example, the communication link is provided between abase station 141 and a mobile device 152. As shown in FIG. 15A, thecommunications link includes a downlink channel used for RFcommunications from the base station 141 to the mobile device 152, andan uplink channel used for RF communications from the mobile device 152to the base station 141.

Although FIG. 15A illustrates carrier aggregation in the context of FDDcommunications, carrier aggregation can also be used for TDDcommunications.

In certain implementations, a communication link can provideasymmetrical data rates for a downlink channel and an uplink channel.For example, a communication link can be used to support a relativelyhigh downlink data rate to enable high speed streaming of multimediacontent to a mobile device, while providing a relatively slower datarate for uploading data from the mobile device to the cloud.

In the illustrated example, the base station 141 and the mobile device152 communicate via carrier aggregation, which can be used toselectively increase bandwidth of the communication link. Carrieraggregation includes contiguous aggregation, in which contiguouscarriers within the same operating frequency band are aggregated.Carrier aggregation can also be non-contiguous, and can include carriersseparated in frequency within a common band or in different bands.

In the example shown in FIG. 15A, the uplink channel includes threeaggregated component carriers f_(UL1), f_(UL2), and f_(UL3).Additionally, the downlink channel includes five aggregated componentcarriers f_(DL1), f_(DL2), f_(DL3), f_(DL4), and f_(DL5). Although oneexample of component carrier aggregation is shown, more or fewercarriers can be aggregated for uplink and/or downlink. Moreover, anumber of aggregated carriers can be varied over time to achieve desireduplink and downlink data rates.

For example, a number of aggregated carriers for uplink and/or downlinkcommunications with respect to a particular mobile device can changeover time. For example, the number of aggregated carriers can change asthe device moves through the communication network and/or as networkusage changes over time.

FIG. 15B illustrates various examples of uplink carrier aggregation forthe communication link of FIG. 15A. FIG. 15B includes a first carrieraggregation scenario 161, a second carrier aggregation scenario 162, anda third carrier aggregation scenario 163, which schematically depictthree types of carrier aggregation.

The carrier aggregation scenarios 161-163 illustrate different spectrumallocations for a first component carrier f_(UL1), a second componentcarrier f_(UL2), and a third component carrier f_(UL3). Although FIG.15B is illustrated in the context of aggregating three componentcarriers, carrier aggregation can be used to aggregate more or fewercarriers. Moreover, although illustrated in the context of uplink, theaggregation scenarios are also applicable to downlink.

The first carrier aggregation scenario 161 illustrates intra-bandcontiguous carrier aggregation, in which component carriers that areadjacent in frequency and in a common frequency band are aggregated. Forexample, the first carrier aggregation scenario 161 depicts aggregationof component carriers f_(UL1), f_(UL2), and f_(UL3) that are contiguousand located within a first frequency band BAND1.

With continued reference to FIG. 15B, the second carrier aggregationscenario 162 illustrates intra-band non-continuous carrier aggregation,in which two or more components carriers that are non-adjacent infrequency and within a common frequency band are aggregated. Forexample, the second carrier aggregation scenario 162 depicts aggregationof component carriers f_(UL1), f_(UL2), and f_(UL3) that arenon-contiguous, but located within a first frequency band BAND1.

The third carrier aggregation scenario 163 illustrates inter-bandnon-contiguous carrier aggregation, in which component carriers that arenon-adjacent in frequency and in multiple frequency bands areaggregated. For example, the third carrier aggregation scenario 163depicts aggregation of component carriers f_(UL1) and f_(UL2) of a firstfrequency band BAND1 with component carrier f_(UL3) of a secondfrequency band BAND2.

FIG. 15C illustrates various examples of downlink carrier aggregationfor the communication link of FIG. 15A. The examples depict variouscarrier aggregation scenarios 164-168 for different spectrum allocationsof a first component carrier f_(DL1), a second component carrierf_(DL2), a third component carrier f_(DL3), a fourth component carrierf_(DL4), and a fifth component carrier f_(DL5). Although FIG. 15C isillustrated in the context of aggregating five component carriers,carrier aggregation can be used to aggregate more or fewer carriers.Moreover, although illustrated in the context of downlink, theaggregation scenarios are also applicable to uplink.

The first carrier aggregation scenario 164 depicts aggregation ofcomponent carriers that are contiguous and located within the samefrequency band. Additionally, the second carrier aggregation scenario165 and the third carrier aggregation scenario 166 illustrates twoexamples of aggregation that are non-contiguous, but located within thesame frequency band. Furthermore, the fourth carrier aggregationscenario 167 and the fifth carrier aggregation scenario 168 illustratestwo examples of aggregation in which component carriers that arenon-adjacent in frequency and in multiple frequency bands areaggregated. As a number of aggregated component carriers increases, acomplexity of possible carrier aggregation scenarios also increases.

With reference to FIGS. 15A-15C, the individual component carriers usedin carrier aggregation can be of a variety of frequencies, including,for example, frequency carriers in the same band or in multiple bands.Additionally, carrier aggregation is applicable to implementations inwhich the individual component carriers are of about the same bandwidthas well as to implementations in which the individual component carriershave different bandwidths.

Certain communication networks allocate a particular user device with aprimary component carrier (PCC) or anchor carrier for uplink and a PCCfor downlink. Additionally, when the mobile device communicates using asingle frequency carrier for uplink or downlink, the user devicecommunicates using the PCC. To enhance bandwidth for uplinkcommunications, the uplink PCC can be aggregated with one or more uplinksecondary component carriers (SCCs). Additionally, to enhance bandwidthfor downlink communications, the downlink PCC can be aggregated with oneor more downlink SCCs.

In certain implementations, a communication network provides a networkcell for each component carrier. Additionally, a primary cell canoperate using a PCC, while a secondary cell can operate using a SCC. Theprimary and secondary cells may have different coverage areas, forinstance, due to differences in frequencies of carriers and/or networkenvironment.

License assisted access (LAA) refers to downlink carrier aggregation inwhich a licensed frequency carrier associated with a mobile operator isaggregated with a frequency carrier in unlicensed spectrum, such asWiFi. LAA employs a downlink PCC in the licensed spectrum that carriescontrol and signaling information associated with the communicationlink, while unlicensed spectrum is aggregated for wider downlinkbandwidth when available. LAA can operate with dynamic adjustment ofsecondary carriers to avoid WiFi users and/or to coexist with WiFiusers. Enhanced license assisted access (eLAA) refers to an evolution ofLAA that aggregates licensed and unlicensed spectrum for both downlinkand uplink.

Acoustic wave devices disclosed herein can have relatively high powerdurability. The relatively high thermal conductivity of the supportsubstrate of the acoustic wave devices disclosed herein can beadvantageous for handling relatively high power in 5G NR applications.For example, acoustic wave devices disclosed herein can dissipate heatassociated with higher TDD duty cycles in 5G NR applications, such aswill be described with reference to FIG. 16B.

FIG. 16A is a schematic diagram of an RF communication system 180 withdynamic waveform control and power boost. The RF communication system180 can correspond to a UE, and is in communication with the basestation 141 at least over a TDD communication link. Although not shownin FIG. 16A for clarity of the figure, the RF communication system 180can wirelessly communicate with the base station 141 over one or moreother communication links, for instance, over one or more FDDcommunication links and/or over one or more additional TDD communicationlinks.

The RF communication system 180 includes a transmitter 182, a transmitchain 184, and an antenna 185. The transmitter 182 can includes, forexample, a gain selection circuit, and a waveform selection circuit. Inone example, the RF communication system 180 further includes a receivechain and a receiver, which process signals received from the antenna185 and/or another antenna.

The transmitter 182 generates an RF signal, which is provided to thetransmit chain 184 for amplification and other signal conditioning. Thetransmit chain 184 includes at least a filter 183, which provides an RFtransmit signal to the antenna 185 for wireless transmission over theTDD communication link. The filter 183 can include one or more of theacoustic devices disclosed herein, such as the SAW resonator 1illustrated in FIG. 1 .

As shown in FIG. 16A, the TDD communication link includes transmit (Tx)and receive (Rx) time slots, such as Tx time slots 186 and Rx time slots188. The Tx time slots 186 corresponding to uplink (UL) communicationsin which the RF communication system 180 is permitted to transmit to thebase station 141 over the TDD communication link. Additionally, the Rxtime slots 188 corresponding to downlink (DL) communications in whichthe RF communication system 180 is permitted to receive transmissionsfrom the base station 141 over the TDD communication link. In certainimplementations, the timing of when the time slots occur is controlledat the network level.

The TDD communication link has a transmit duty cycle corresponding to afraction of the time slots dedicated to UL communications. For instance,in this example shown in FIG. 16A, the transmit duty cycle is 25%corresponding to about one-quarter of the time slots dedicated totransmit communications. In the example shown in FIG. 16A, transmitcommunications are uplink communications. Although an example with a 25%transmit duty cycle is shown, the transmit duty cycle of a TDDcommunication link can have a variety of different values and can changeover time with network usage, radio environment, and/or a variety ofother factors. In certain implementations, the TDD communication linkcorresponds to wireless communications over at least one 3GPP frequencyband, such as a 5G NR band.

FIG. 16B is a schematic diagram of the RF communication system 180 withdynamic waveform control and power boost transmitting with a differenttransmit duty cycle from the duty cycle shown in FIG. 16A. In certain 5GNR applications, higher TDD transmit duty cycles are implemented than in4G LTE applications. Since transmit power is higher than receive power,higher TDD transmit duty cycles lead to higher power. The acoustic wavedevices disclosed herein can be advantageous in handling such higherpower. In FIG. 16B, the transmit duty cycle is 75% corresponding tothree-quarters of the time slots dedicated to TDD transmitcommunications. In certain implementations, the TDD communication linkcorresponds to wireless communications over at least one 3GPP frequencyband, such as a 5G NR band.

There can be higher peak to average power ratios in 5G NR applicationsthan in 4G LTE applications. The relatively high power durability ofacoustic wave devices disclosed herein can be advantageous in suchhigher peak to average power ratio applications. Peak to average powerration will be discussed with reference to FIGS. 17A to 17B.

FIG. 17A is a graph illustrating one example of an RF signal waveformversus time. The graph depicts the RF signal waveform, the envelope ofthe RF signal, the average signal power, and the peak signal power. Thepeak to average power ratio (PAPR) or crest factor of the RF signalwaveform corresponds to the ratio of the waveform's peak signal power tothe waveform's average signal power.

FIG. 17B is one example of a PAPR complementary cumulative distributionfunction (CCDF) for various cyclic prefix orthogonal frequency divisionmultiplexing (CP-OFDM) waveforms relative to a single carrier frequencydivision multiple access (SC-FDMA) reference waveform.

As shown in FIG. 17B, the PAPR CCDF is shown for a variety of modulationorders and bandwidths of CP-OFDM 5G NR waveforms. For the examplewaveforms shown, higher order modulations and wider signal bandwidthdoes not substantially increase PAPR, but rather the CP-OFDM waveformshave similar PAPR to one another.

When comparing 5G NR CP-OFDM waveforms to the reference LTE SC-FDMA QPSKwaveform it can be seen that the 5G NR waveforms exhibit higher PAPR ofabout 3 dB or more. Higher PAPR can increase power handling demands onacoustic wave filters. The higher PAPR also raises a linearityconstraint for a power amplifier. Moreover, for UE operating at a celledge and/or with poor SNR, higher PAPR can constrain output power and/orincrease battery current.

Although embodiments disclosed herein relate to surface acoustic waveresonators, any suitable principles and advantages disclosed herein canbe applied to other types of acoustic wave resonators, such as Lamb waveresonators and/or boundary wave resonators and/or any other types ofacoustic wave devices.

Any of the embodiments described above can be implemented in associationwith mobile devices such as cellular handsets. The principles andadvantages of the embodiments can be used for any systems or apparatus,such as any uplink wireless communication device, that could benefitfrom any of the embodiments described herein. The teachings herein areapplicable to a variety of systems. Although this disclosure includessome example embodiments, the teachings described herein can be appliedto a variety of structures. Any of the principles and advantagesdiscussed herein can be implemented in association with RF circuitsconfigured to process signals in a frequency range from about 30 kHz to300 GHz, such as in a frequency range from about 450 MHz to 8.5 GHz.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as die and/or acoustic wave filter assembliesand/or packaged radio frequency modules, uplink wireless communicationdevices, wireless communication infrastructure, electronic testequipment, etc. Examples of the electronic devices can include, but arenot limited to, a mobile phone such as a smart phone, a wearablecomputing device such as a smart watch or an ear piece, a telephone, atelevision, a computer monitor, a computer, a modem, a hand-heldcomputer, a laptop computer, a tablet computer, a personal digitalassistant (PDA), a microwave, a refrigerator, an automobile, a stereosystem, a DVD player, a CD player, a digital music player such as an MP3player, a radio, a camcorder, a camera, a digital camera, a portablememory chip, a washer, a dryer, a washer/dryer, a copier, a facsimilemachine, a scanner, a multi-functional peripheral device, a wrist watch,a clock, etc. Further, the electronic devices can include unfinishedproducts.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. Additionally, thewords “herein,” “above,” “below,” and words of similar import, when usedin this application, shall refer to this application as a whole and notto any particular portions of this application. Where the contextpermits, words in the above Detailed Description using the singular orplural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

Moreover, conditional language used herein, such as, among others,“can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and thelike, unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or states. Thus, such conditional language is notgenerally intended to imply that features, elements and/or states are inany way required for one or more embodiments.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

What is claimed is:
 1. An acoustic wave device comprising: a supportsubstrate; a ceramic layer over the support substrate, the ceramic layerhaving a thickness that is at least equal to or greater than awavelength A of the acoustic wave device to suppress spurious modesresulting from back scattering, the support substrate having a higherthermal conductivity than the ceramic layer; a piezoelectric layer overthe ceramic layer; and an interdigital transducer electrode over thepiezoelectric layer, the acoustic wave device configured to generate anacoustic wave.
 2. The acoustic wave device of claim 1 wherein thesupport substrate is a single crystal layer.
 3. The acoustic wave deviceof claim 1 wherein the support substrate includes silicon.
 4. Theacoustic wave device of claim 1 wherein the acoustic wave has awavelength of λ, and the piezoelectric layer has a thickness in a rangefrom 3λ to 40λ.
 5. The acoustic wave device of claim 1 wherein theceramic layer includes polycrystalline spinel.
 6. The acoustic wavedevice of claim 1 wherein a surface of the ceramic layer has a surfaceroughness in a range from 0.1 nanometers to 2 nanometers.
 7. Theacoustic wave device of claim 6 wherein the ceramic layer and thepiezoelectric layer are directly bonded to each other without anintervening layer.
 8. The acoustic wave device of claim 1 wherein theceramic layer and the support substrate are bonded to each other by wayof an adhesive.
 9. The acoustic wave device of claim 1 furthercomprising a temperature compensation layer over the interdigitaltransducer electrode.
 10. The acoustic wave device of claim 1 whereinthe piezoelectric layer includes lithium based piezoelectric layer. 11.The acoustic wave device of claim 1 wherein the ceramic layer isarranged to scatter back reflections of the acoustic wave.
 12. Anacoustic wave device comprising: a support substrate; a polycrystallinespinel layer over the support substrate, the polycrystalline spinellayer having a thickness that is at least equal to or greater than awavelength λ of the acoustic wave device to suppress spurious modesresulting from back scattering, the support substrate has a greaterthermal conductivity than the polycrystalline spinel layer; apiezoelectric layer over the polycrystalline spinel layer; and aninterdigital transducer electrode over the piezoelectric layer, theacoustic wave device configured to generate an acoustic wave.
 13. Theacoustic wave device of claim 12 further comprising a temperaturecompensation layer over the interdigital transducer electrode.
 14. Theacoustic wave device of claim 12 wherein the support substrate includessilicon.
 15. The acoustic wave device of claim 12 wherein the supportsubstrate is thicker than the polycrystalline spinel layer.
 16. Theacoustic wave device of claim 12 wherein a surface of thepolycrystalline spinel layer has a surface roughness in a range from 0.1nanometers to 2 nanometers.
 17. The acoustic wave device of claim 16wherein the polycrystalline spinel layer and the piezoelectric layer arebonded to each other without an intervening layer.
 18. The acoustic wavedevice of claim 12 wherein the acoustic wave has a wavelength of λ, andthe piezoelectric layer has a thickness in a range from 3λ to 40λ.
 19. Asurface acoustic wave filter comprising: a surface acoustic waveresonator including a support substrate, a ceramic layer over thesupport substrate, a piezoelectric layer over the ceramic layer, and aninterdigital transducer electrode over the piezoelectric layer, theceramic layer having a thickness that is at least equal to or greaterthan a wavelength λ of the surface acoustic wave resonator to suppressspurious modes resulting from back scattering; and a plurality of othersurface acoustic wave resonators, the surface acoustic wave resonatorand the plurality of other surface acoustic wave resonators togetherarranged to filter a radio frequency signal.
 20. The surface acousticwave filter of claim 19 wherein the ceramic layer is a polycrystallinespinel layer.